This invention relates to a drive arrangement and in particular to a drive arrangement suitable for use in driving the control surfaces of an aircraft wing.
Each wing of a large aircraft typically carries two or more high-lift, trailing edge control surfaces or flaps which are moved, simultaneously and at the same speed, from a stowed position to a deployed position to increase lift, for example when the aircraft is travelling at relatively low speeds such as during take-off and landing. Often, a single synchronized drive arrangement is used to drive the flaps for movement. It is usual to incorporate arrangements operable such that, in the event of a failure or breakage in the drive arrangements associated with the flaps, the flaps are held against movement so as to avoid the occurrence of a so-called skew condition that can adversely affect the stability of the aircraft. A number of arrangements are known which, for example, link the adjacent ends of the flaps to one another to prevent or restrict relative movement therebetween, and which cause the drive arrangements associated with the flaps to be locked against further movement in the event that it is detected or sensed that one or more of the flaps is becoming skewed, thereby avoiding worsening the skew. U.S. Pat. No. 4,715,567 describes an arrangement of this general type.
Where modern composite materials are used in the wing, and for accelerated trailing edge vortex decay, it has been found to be desirable to move the flaps on the wing at different times and/or through different distances and/or at different speeds, whilst maintaining symmetry between the wings. For example, it may be desired to deploy the inboard flaps of each wing whilst holding the outboard flaps in their stowed positions. Such an operating mode will typically result in less bending or flexing of the wing due to the majority of the applied aerodynamic loading occurring close to the wing roots, less being applied towards the wing tips.
Clearly, as the adjacent flaps do not move simultaneously and at the same speed, known systems which rely on locking together and/or sensing relative movement between the adjacent edges of a pair of flaps cannot be used to sense or avoid a skew condition. Further, the requirement to allow the flaps to be driven independently prevents the known synchronous drive arrangement from being used.
The use of separate motor driven actuators adjacent each end of each flap has been considered. For example, by using a dual load path type actuator, a separate tie bar is able to transmit applied loadings, preventing uncontrolled movement of the flap, in the event of an actuator failure. However, such actuators are relatively heavy and so the provision of two such actuators associated with each flap is undesirable.